Effects of background‐noise on speech listening difficulty in reverberant sound fields

Abstract

The previous work [M. Morimoto et al., J. Acoust. Soc. Am. 108, 2633 (2000)] demonstrated that the listening difficulty can evaluate the quality of speech transmission more exactly and sensitively than intelligibility. In the present work two listening tests were performed to investigate the effects of background noise on the listening difficulty in reverberant sound fields. In the tests, both the listening difficulty and the intelligibility were assessed using word lists based on word familiarity. In the first test, the background noise level was changed, while the speech level was constant at 55 dBA. In the second test, both the speech and background noise levels were changed in the same manner, keeping the signal to noise ratio constant. The results of both tests supported the previous results. Furthermore, the results of the first test indicated that the difficulty did not always increase when background noise levels exceeded the absolute threshold of the noise. Namely, background noise lower than about 30 dBA does not increase the difficulty. The results of the second test demonstrated that the optimum signal to noise ratio depended on background noise level. Overamplifying speech to keep the signal to noise ratio constant increases the difficulty, though the intelligibility does not decrease.